Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular telephones. Program code and system data such as a basic input/output system (BIOS) are typically stored in flash memory devices for use in personal computer systems.
FIG. 1 illustrates a cross-sectional view of a typical prior art memory cell having a metal-insulator-metal architecture. This cell has two source/drain regions 101 and 102 that are doped into a silicon substrate 100. A gate insulator layer 104 is formed over the channel between the source/drain regions 101 and 102. A polysilicon layer 106 and metal layer 107 make up the floating gate 120 that stores the charge for the cell. A metal oxide acts as the intergate insulator 108 between the floating gate 120 and the metal control gate 110.
In order to write data into the cell illustrated in FIG. 1, tunneling or hot electron injection would typically be used through the gate oxide 104. Tunneling or hot electron injection can cause a degradation of the transistor's characteristics, leading to read errors, after a number of program and erase cycles.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a flash memory that reduces degradation due to program/erase cycles.